Many systems and circuits utilize temperature sensing elements (TSEs) to determine a temperature of a device. For example, typical temperature dependent resistive devices (TDRD) such as thermistors may have resistances that are inversely proportional to temperature. By measuring the resistance of the thermistor, the temperature of the thermistor can be determined. As a result, temperatures of components and devices near the thermistor can also be determined or estimated. Resistance sensing techniques are sometimes used as identification techniques to determine the identity of a device, module, or other peripheral unit that is connected to a main device or main assembly. For example, portable communication devices that accept more than one type of modular battery include a battery identification technique to determine the type of battery that is connected to the portable communication device. In order to minimize components and contacts, conventional designs often combine temperature sensing techniques and identification techniques. For example, some conventional portable communication devices that accept more than one type of modular battery include a temperature sensing mechanism that connects to circuits within the battery packs to determine temperature and to identify the battery module. Each type of battery module includes thermistor circuits having different characteristics allowing the portable communication device to identify the particular battery module that is connected. Typically, each thermistor circuit has a resistance to temperature relationship that is offset from relationships of other thermistor circuits within other types of battery modules. Conventional systems are limited, however, in that the resistance-to-temperature relationships of different circuits typically overlap. FIG. 1, for example, is a graphical illustration showing two curves 102, 104 representing the resistance vs. temperature relationship for two conventional battery modules where the curves overlap. The overlap region 106 results in ambiguous data since a measurement of a resistance within the overlap region is associated with both of the curves 102, 104. The measurement may correspond to one type of battery module at a low temperature or another type of battery module at a higher temperature. For example, resistance R may correspond to a temperature of T1 if one battery module is used and a temperature of T2 if another battery is connected. This error could lead to catastrophic results. A battery could explode where a battery module is inaccurately identified and an incorrect charging scheme is applied. Further, the dynamic range and accuracy of the temperature measuring circuit is reduced as the number of identification devices is increased as well as requiring a unique voltage to temperature transfer function for each of the possible curves. In addition, these problems are exacerbated as the number of IDs is increased.
Accordingly, there is a need for an apparatus, system and method for identification with temperature dependent resistive devices.